Various feeding devices for grainy or fragmented material are known, the material being fed in for further treatment without any great increase of pressure, or for further treatment under an essentially increased pressure. An example of the first mentioned treatment is feeding fuel into a fludized bed as described in the publication EP-Al-0219686. In this case the fuel is fed in from a charging bin by means of a first plane slide which moves the fuel from the charge bin laterally to a position in front of a cylindrical input slide. Finally, said last mentioned slide feeds the fuel through an opened side gate into the fuel chamber. The fuel is fed into the fuel chamber without any actual overpressure.
In order to feed disintergrated material against a comparatively high pressure for further treatment of the material, as for example gasifying, some form of lock-passing or sluicing is exercised when feeding in. The publication SE-B-456 645 examplifies such an apparatus. In this case the material is supplied for treatment from a charging bin to a first receiving chamber and is removed therefrom, by means of a feed piston or a feed screw, and introduced into the input chamber proper through a valve device. By means of a feeder piston in the input chamber the material is introduced into a following high pressure chamber through a further valve. The two valves cooperate in order to bring about sluicing of the material into the high pressure side. The final feeding into the high pressure chamber takes place by means of said piston. The device is especially directed towards input sluicing of wet bio mass, such as e.g. damp peat having up to 20% dry substance, into a high pressure reactor operating at a pressure of up to 150 bar and a temperature of 350.degree. C. In order to ensure complete discharge of the peat from the actual input chamber (sluice chamber) into the reactor on the high pressure side the feed piston is moved past the closing member of the output valve. This known device operates by in-feed in two steps, namely, a first feeding in from the receiving chamber to the actual input chamber and a following final in-feed step from this chamber against the action of high pressure. Said last mentioned in-feed step is exercised by means of a conventional feed piston.
The present invention is directed in particular towards the in-feed of wood ships and similar comparatively dry compactible material. To this end the possibility is utilized to receive and compact the material in one single operating chamber and to discharge the material therefrom into a collecting container under pressure by means of a single active member in the form of a screw piston moving under programmed control. The in-feed process according to the invention is then characterized by a series of operational steps according to the following:
a) the material is supplied to the input chamber through the opened input valve by means of a feeding piston axially movable in the input chamber, the feeding piston having the form of a screw piston which is located in an axially retracted, receiving position, opposite to the input valve, and which feeds, while rotating in an axially stationary position, the material into the chamber towards the closed output valve,
b) material is formed as a compacted plug in the exit end of the chamber in front of the closed output valve,
c) the input valve is closed and the rotation of the screw piston terminated,
d) the output valve is opened and the material plug formed is pushed, by the screw piston being moved axially, into the collecting container through a slightly expanding pressure tube whose internal wall has serrations serving to prevent return movement of the plug,
e) the screw piston is retracted a short distance to permit the output valve to close,
f) the output valve is closed and the screw piston is pulled back to its starting position while rotating in the same direction as when feeding in material and in correspondence to the pitch of the screw piston, and
g) the input valve is opened.
The in-feed procedure according to the invention has the advantage that the constructive design of the corresponding apparatus is highly simplified, in that only three operatively active parts are necessary for handling the material, namely, an input valve, a screw piston and an output valve. Hereby the in-feed device is highly simplified. The desired translatory displacement of the material is secured by the feature that during the in-feed procedure the screw piston is at first merely rotated for transporting axially the material into the chamber in order to build up a compacted material plug in front of the screw piston, to then be moved axially without rotation in order to discharge the material plug thus formed in front of the screw piston and, finally, to return to its starting position while rotating in the same direction. In other words, unnessary and power consuming rotation of the material in the chamber is avoided.
The arrangement of a single screw piston for transporting and compacting the treated material renders a simple and rational build-up of the whole apparatus possible, including the requested member for axially displacing the screw piston along a single common axis. To perform this the screw piston is carried for rotation and axial displacement in a guide piston which is slideably carried in an elongated part of the input chamber. The guide piston is displaced axially by means of a hydraulic cylinder connected to the elongated part of the input chamber, the rotational shaft of the screw piston extending axially through a tubular, guide piston-connected piston rod of the hydraulic cylinder, said shaft being connected at its free end to a device for controlling the rotational position of the screw piston.
The guide piston is provided with guide keys engaging axial groves in the internal wall of the input chamber. Besides its primary function of preventing rotation of the guide piston the grooves also serve for preventing rotation of the treated material under the action of the screw piston while this is rotating.
The compacted material plug discharged is forwarded to a collecting container through a slightly expanding pressure tube having a serrated internal profile. The tube allows the compacted material plug to undergo a certain elastic relaxation and prevents the plug, thanks to its uni-directed saw-teeth, from being returned towards the input chamber by possible pressure effect on the output side.
The invention will be described below by way of example and with reference to the accompanying drawing which illustrates an apparatus according to the invention: